The present invention relates to a control valve for maintaining the viscosity respectively the temperature of pressure fluid in a hydraulic arrangement substantially constant by throttling the flow of pressure fluid at a control slide and with an element influenced by the temperature of the pressure fluid, whereby downstream of the control slide a precontrol valve is arranged which receives the aforementioned element and which controls an additional throttling connection from the inlet to the outlet of the valve. In a known control valve of the aforementioned kind it happens sometimes that air passes from the source of pressure fluid into the valve, whereby the action of the temperature influenced element will be disturbed, which may lead to operating trouble due to overheating of the pressure fluid. It may also happen that when the pressure fluid, especially oil, is contaminated, foreign particles pass in a throttle bore in the control slide, which will disturb the proper function of the valve.